Radiation-induced attenuation in single-mode pure-silica-core optical fibers two years after high-fluence reactor irradiation

Abstract

Single-mode pure-silica-core optical fibers (PSFs) coated with different materials (aluminum, copper, polyimide, or acrylate) and reactor-irradiated 2 years ago to the fast-neutron fluence of 1.8·1020n/cm2 and γ-dose of 2.3·109 Gy with evacuation to 0.005–0.25 Pa were OTDR-tested at wavelengths λ = 1.31 and 1.55 µm. Metal-coated PSFs demonstrated virtually the same radiation-induced attenuation (RIA) at λ = 1.55 µm as was measured 1 day after the irradiation (∼2–4 dB/m), whereas RIA in the polyimide-coated PSF that survived the irradiation went down from ∼4.3 to 1.8 dB/m. Fiber microbending originating from radiation-induced coating decay (not mechanical failure of the fiber itself) was argued to be the source of the catastrophic RIA rise in the polyimide- and acrylate-coated PSFs during the reactor irradiation in vacuum.